Importance of Angle-dependent Partial Frequency Redistribution in Hyperfine Structure Transitions Under Incomplete Paschen-Back Effect Regime

TL;DR

This paper develops a detailed polarized line transfer model incorporating angle-dependent partial frequency redistribution (AD-PRD) for hyperfine structure transitions, accounting for magnetic fields and collisions, with implications for solar spectrum analysis.

Contribution

It introduces a comprehensive solution for polarized line transfer with AD-PRD in hyperfine structure, including magnetic field effects and elastic collisions, advancing modeling accuracy.

Findings

AD-PRD effects are significant below 30G magnetic fields.

Angle-averaged PRD is sufficient for stronger fields.

The model applies to Na I D2 line in solar spectrum.

Abstract

Angle-frequency coupling in scattering of polarized light on atoms is represented by the angle-dependent (AD) partial frequency redistribution (PRD) matrices. There are several lines in the linearly polarized solar spectrum, for which PRD combined with quantum interference between hyperfine structure states play a significant role. Here we present the solution of the polarized line transfer equation including the AD-PRD matrix for scattering on a two-level atom with hyperfine structure splitting (HFS) and an unpolarized lower level. We account for the effects of arbitrary magnetic fields (including the incomplete Paschen-Back effect regime) and elastic collisions. For exploratory purposes we consider a self-emitting isothermal planar atmosphere and use atomic parameters that represent an isolated Na\,{\sc i} D$_2$ line. For this case we show that the AD-PRD effects are significant for field strengths below about 30G, but that the computationally much less demanding approximation of angle-averaged (AA) PRD may be used for stronger fields.